Epoxy resins are excellent in heat resistance, adhesiveness, water resistance, mechanical strength, electric properties and so on, and thus have been used for sealing resins, panel laminating resins, coating materials, adhesives, inks, various sealing materials, and the like. As a method for curing epoxy resins, there has been known a light heat-curing system by cationic polymerization. Recently, cationic polymerization using an oxetane resin having an oxetanyl group in the molecular chain, besides an epoxy resin, has been widely investigated.
An oxetane resin has the following characteristics in comparison with an epoxy resin: (1) it is excellent in forming high molecular weight and material properties because the propagation reaction of polymerization is rapid; (2) it is excellent in processabilty and stability because an oxetanyl group does not have mutagenecity; and, (3) it is excellent in electric properties and moisture resistance because the generation of hydroxyl groups by polymerization is low. In addition to the above characteristics, the oxetane resin has the characteristics such as low curing shrinkage, low skin stimulation and inertness to oxygen, in comparison with a radical-polymerization system.
However, it has been difficult to use an oxetane resin alone because the initiation reaction is slow. Saegusa et al. ‘Japanese Journal of Industrial Chemistry, 66, 474 (1963)’ has reported that the curing rate was improved by adding an epoxy resin to an oxetane resin. In addition, Sasaki ‘Radtech 2000, 61 (2000)’ has reported that the initiation reaction occurred by an epoxy group and then the propagation reaction by an oxetanyl group was carried out, consequently accomplishing fast curing.
Further, Aoshima et al. ‘Journal of Polymer Science Part A: Polymer Chemistry, 1719-1728, Volume 32, Issue 9’ has reported that the polymerization of a vinyl ether is carried out in the manner of living polymerization when tetrahydrofuran as a cyclic ether is added to a cationic polymerization system using a vinyl ether and an alkylaluminum halide compound as a Lewis acid catalyst. However, they have also reported that when a compound having an oxetanyl group or an oxilane ring is added, the polymerization of a vinyl ether does not occur even in the same cyclic ether and polymer cannot be thus obtained.
[Patent Document 1] JP-A No. 1995-053711
[Patent Document 2] JP-A No. 1995-062082